The term broadband covers a host of new products, technologies, services, and networks. One way to define broadband networks is to categorize them as those networks that support services requiring bit rates well above one megabits per second. Business and residential subscribers will be connected to broadband networks via a common access, operating at 150 megabits per second or above, that can handle a range of different broadband service types. ATM (asynchronous transfer mode) has been chosen as the communication principle on which broadband networks will be based. A future broadband ISDN (integrated services digital network) will offer the flexibility needed to handle diverse services ranging from basic telephone service to high speed data transfer, videotelephony, and high quality television distribution. The key to this flexibility is ATM which carries digital information in special cells. This allows the network to be used efficiently by applications and services with widely differing bandwidth requirements and call characteristics.
ATM cells have a five-byte header and a 48-byte payload. The header includes the routing information for the packet. It is important to compare this routing information to many possible values very rapidly. For example, if the bit rate is 155 megabits per second, an eight-byte header corresponds to approximately 0.25 microseconds. It is desirable to make the routing decision in this very short time period. What is needed is an apparatus capable of making very fast comparisons.